(1) Field of the Invention
This invention relates to light source, particularly to the use of multi-color light emitting diode (LED) light source to produce a white light.
(2) Brief Description of Related Art
FIG. 1A shows a prior art to produce a colorless white light. The light source uses three color LEDs to produce a white light. A red color LED R, a green color LED G, and a blue color LED B are mounted on a substrate 10, The three LEDs are then covered with a glue for protection.
FIG. 1B shows the color spectrum of such a light source. The red LED has a light spectrum with wavelength in the 580 nm-680 nm range and a peak at 640 nm. The green LED has a light spectrum with wavelength in the 480 nm-580 nm range and a peak at 530 nm The blue LED has a light spectrum with wavelength in the 430 nm-530 nm range and a peak at 480 nm. The white light in nature has light spectrum ranging from 400-780 nm wavelength The artificial white light source using the R, G, B LEDs has peaks at 640 nm, 530 nm and 480 nm wavelengths, but lacks light spectrum below 430 nm wavelength, around 500 nm wavelength, around 580 nm wavelength and above 680 nm wavelength. Therefore, the combination of three color LEDs does not reproduce a true colorless light.